The cellular telephone industry has made phenomenal strides in commercial operations in the United States as well as the rest of the world. Growth in major metropolitan areas has far exceeded expectations and is outstripping system capacity. If this trend continues, the effect of rapid growth will soon reach even the smaller markets. Innovative solutions are required to meet these increasing capacity needs as well as to maintain high quality service and to avoid rising prices.
Throughout the world, one important step in cellular systems is to change from analog to digital transmission. Equally important is the choice of an effective digital transmission scheme for implementing the next generation of cellular technology. Furthermore, it is widely believed that the first generation of personal communication networks (PCN), (employing low cost, pocketsize, cordless telephones that can be carried comfortably and used to make or receive call in the home, office, street, car, etc.), will be provided by the cellular carriers using the next generation digital cellular system infrastructure and the cellular frequencies.
A key feature demanded in these new system is increased traffic capacity. Currently, cellular mobile telephone systems divide a region to be covered into cells. The modulation system used in current cellular radio systems is called Frequency Division Multiple Access (FDMA), in which each cell is allocated a set of frequencies which are different from the frequencies used in neighboring cells. Each frequency in the FDMA system only carries one conversation, and therefore the reuse of a frequency in another cell is only permitted when it is a sufficient distance away from the first cell so that interference does not occur. In FDMA cellular systems, one frequency per cell is dedicated to be a so-called calling channel. The frequency of the calling channel the frequency a mobile monitors when the mobile station is in an idle condition, and is used by the network to call mobiles when a conversation is originated by the network. A corresponding uplink frequency (mobile to base) is available for use by the mobile to originate calls. The FDMA calling channel also carries information about neighboring cells' calling channel frequencies and also identifies the cell in the network.
In the United States and Europe, time division multiple access (TDMA) is about to be introduced for the provision of cellular mobile telephone services. In the United States' system, the FDMA calling channel is retained as the method by which calls are initiated. In the European GSM system, the TDMA format provides eight time slots on each 200 kHz-wide frequency channel. One of these eight time slots on one of the frequency channels of each cell is designated as a calling channel. The information carried on the TDMA calling channel includes TDMA synchronization information, details about surrounding cells and calls to specific mobiles.